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Hell everyone,
I've got this black marks on the bedroom ceiling. Looks like it happened over a period of time (not overnight).
I've asked roofer to check whether any leaking in the ceiling and confirmed there is no leak at all.
I live in Southeast Brisbane if the location is matters.
Any idea what this could be and how to solve it? 
Hi @ppp,
My first thoughts are that it's likely mould growth over the cooler months, though the image isn't of high enough quality for me to determine whether the stain is on the paint or a watermark coming from the sheeting behind. If bedrooms are not well-ventilated, condensation forms on surfaces, and you can get thin mould growth such as this. There doesn't need to be a leak, and the moisture from breath can be enough for it to start.
I recommend spraying a section with bleach and then cleaning it down. If the area whitens and the darker stain is removed, it indicates mould growth on the surface. You can either clean the ceiling periodically to remove it or follow this guide: How to paint a mouldy ceiling.
Please let me know if you have any questions.
Mitchell
